The present invention relates in general to RDS radios having dual tuners, and more specifically to a dual mode radio for operating in both a diversity and a non-diversity mode to minimize the effects of multipath distortion while maintaining efficient collection of RDS related information, including collecting signal quality data for RDS alternate frequencies.
Space diversity radio receiver systems can be employed to reduce the effects of multipath distortion in mobile receivers. Multipath distortion is a localized effect resulting from interaction between multiple signals from a single transmitter that have traversed different paths to reach a receiving antenna. By switching between spaced antennas in a diversity radio receiver, specific multipath events can be avoided since the spacing of the antennas helps insure that not both of the antennas will experience the same multipath event at the same time.
The prior art has also shown that separate tuners may be connected to each antenna and that the tuner output signals can be combined to provide improved diversity reception.
Separate tuners have also been employed in radio data system (RDS) receivers. In the case of RDS receivers, however, the tuners simultaneously receive at different frequencies. Standard RDS broadcasts transmit auxiliary digital data within the radio signal in order to achieve various automatic functions of the receiver. The data transmitted on a subcarrier includes alternate frequencies (AFs) at which the identical audio program can be heard. Thus, the receiver can automatically monitor AFs to determine whether a stronger or higher quality signal can be received by switching the tuner to a different frequency (e.g., as a vehicle moves relative to the broadcast transmitters). In an RDS receiver having just a single tuner, AFs can only be checked by briefly switching the tuner to an AF to detect its signal strength and then quickly returning to the original frequency before any detectable break is heard in the reproduction of the original broadcast. In RDS receivers having a second tuner, the second tuner is dedicated to collecting information about AFs (i.e., is not used for audio reproduction) and can monitor any alternate frequencies for as long as desired.
Based on the AF information which is collected and stored in memory in the receiver, the tuner which is reproducing audio signals can be switched to the strongest AF whenever the currently received signal becomes degraded. However, the response time required to detect signal degradation (such as a multipath event) and then to switch to an AF is too slow to prevent distortion from being heard. Thus, a dual tuner RDS radio system is needed which obtains RDS data gathering while providing improved immunity to multipath distortion.